The invention relates to add-on aerodynamic air deflectors for the rear surface of a transport trailer. Inflatable drag reducers have been described (e.g. McDonald (1977) U.S Pat. No. 4,006,932, Ryan (1998) U.S. Pat. No. 5,823,610), and are more practical than rigid versions (e.g. Lechner (1994) U.S. Pat. No. 5,375,903, Switlik (1996) U.S. Pat. No. 5,498,059, Boivin (2001) U.S Pat. No. 6,257,654 B1), because inflatables are light-weight and collapsible to a very thin state so as not to interfere with complete trailer door opening which is important because there is limited room to maneuver at most loading docks. However, given that the standard long-haul trailer in North America is a double door configuration, this requires that the drag reducer have two separate halves meeting medially along a planar surface when inflated. The external surfaces over which the airstream passes should also be planar for minimum turbulence creation and maximum drag reduction. Inflatables naturally tend towards a spherical shape without an internal means of controlling the position of the surface. The present invention describes a novel configuration of internal cords that allows the two bags to meet neatly along a common plane, while having grossly flat external surfaces that are held firmly in place even in heavy crosswinds.
To achieve auto-inflation the present invention employs a flexible air-scoop extending above the roofline from each bag to capture air pressure from the over-passing air stream. Similar such means have been used for inflation purposes in prior art (e.g. McDonald (1977) U.S. Pat. No. 4,006,932, Keedy (1979) U.S. Pat. No. 4,142,755, Lechner (1994) U.S. Pat. No. 5,375,903).
To achieve bag stability and avoid surface flailing during inflation and deflation, an elastic cord oriented in a circular fashion on the medial surface of each bag is employed as disclosed in Andrus (1993) U.S. Pat. No. 5,236,347. The present disclosure further teaches that the placement of such an elastic cord for a double bag configuration is best on the medial surface of each bag thereby drawing the bags together and away from traffic during conditions of partial inflation.
The invention solves the problem of creating an aerodynamically optimal shape with flat surfaces from a soft inflatable material, as well as the problem of the inherent lateral instability of a double bag configuration. The novel aspect disclosed herein is a network of internal cords consisting of a radially oriented array of horizontal cords that stabilize and flatten the lateral surfaces of the bags, and a parallel array of vertical cords that flatten the upper and lower surfaces.